Valve timing control apparatus of internal combustion engine

ABSTRACT

In a valve timing control apparatus employing a helical torsion spring attached at one end to a vane rotor and attached at the other end to a housing, for biasing the vane rotor relative to the housing in a specified phase-change direction under a preload, adjacent coils of the torsion spring being brought into contact with each other at a part of the torsion spring in a circumferential direction under a state where the torsion spring is loaded, a back-pressure relief passage is configured to discharge working oil in a back-pressure chamber of a lock mechanism. The back-pressure relief passage is provided at a predetermined circumferential position that goes across a coil-to-coil contact part that the adjacent coils of the torsion spring are brought into contact with each other when the vane rotor rotates relative to the housing by a maximum angular displacement.

TECHNICAL FIELD

The present invention relates to a valve timing control apparatus of aninternal combustion engine configured to variably control valve timingof an engine valve (intake and/or exhaust valves) depending on anoperating condition of the engine.

BACKGROUND ART

One such valve timing control (VTC) apparatus has been disclosed inJapanese Patent Provisional Publication No. 2005-325749 (hereinafter isreferred to as “JP2005-325749”). In the VTC apparatus disclosed inJP2005-325749, a helical torsion spring is interleaved between a housingand a vane rotor such that the centerline of the helical torsion springis arranged to be substantially coaxial with the rotation axis of therotor, for enabling a biasing force of the torsion spring to act therotor to oppose the rotating load of the rotor relative to the housing,produced by a valve-spring reaction force (i.e., a force acting tophase-retard an angular phase of a camshaft relative to an enginecrankshaft) during operation of the valve operating system of theengine. This contributes to superior operating characteristic andenhanced responsiveness of the VTC apparatus.

SUMMARY OF THE INVENTION

However, when the helical torsion spring is loaded in its windingdirection, the torsion spring deforms, so that the distance betweenadjacent coils (adjacent turns of wire) of a certain circumferentialpart of the coiled spring portion of the torsion spring narrows and thedistance between the adjacent coils of the diametrically-opposed part ofthe coiled spring portion widens. At this time, the deformed helicaltorsion spring tends to incline with respect to the axis (thecenterline) of the torsion spring. As a result of this, in the case ofthe prior-art VTC apparatus, a coil-to-coil contact tends to occur atthe circumferential part of the coiled spring portion having thenarrowed coil-to-coil distance. Such a coil-to-coil contact leads to theproblem of undesirable wear of the helical torsion spring.

It is, therefore, in view of the previously-described drawbacks of theprior art, an object of the invention to provide a valve timing control(VTC) apparatus of an internal combustion engine configured to suppressa helical torsion spring from being worn owing to a coil-to-coilcontact, even in the presence of occurrences of the coil-to-coil contactof the torsion spring, loaded and deformed during operation of the VTCapparatus.

In order to accomplish the aforementioned and other objects of thepresent invention, a valve timing control apparatus of an internalcombustion engine comprises a housing adapted to be driven by acrankshaft of the engine, and configured to define a plurality ofworking-fluid chambers therein by partitioning an internal space by aplurality of shoes protruding radially inward from an inner peripheralsurface of the housing, a vane rotor having a rotor adapted to befixedly connected to a camshaft and a plurality of radially-extendingvanes formed on an outer periphery of the rotor for partitioning each ofthe working-fluid chambers of the housing by the shoes and the vanes todefine phase-advance working chambers and phase-retard working chambers,the vane rotor being configured to phase-advance relative to the housingby supplying hydraulic pressure to each of the phase-advance workingchambers and by discharging working oil in each of the phase-retardworking chambers and configured to phase-retard relative to the housingby supplying hydraulic pressure to each of the phase-retard workingchambers and by discharging working oil in each of the phase-advanceworking chambers, and also configured to have a cylinder structural boreformed in at least one of the plurality of vanes as a through holeextending in a direction of a rotation axis of the vane rotor, a lockmechanism having a lock member slidably installed in the cylinderstructural bore and a biasing member for biasing the lock member in itsextended direction from the vane rotor, the lock mechanism beingconfigured to permit the lock member to be displaced in its retracteddirection against a biasing force of the biasing member by hydraulicpressure acting on the lock member, an engaging recess formed in thehousing so as to oppose the lock member, for restricting rotary motionof the vane rotor relative to the housing by bringing the lock memberinto engagement with the engaging recess with sliding motion of the lockmember in the extended direction, a helical torsion spring attached atone end to the vane rotor and attached at the other end to the housing,for exerting a biasing force on the vane rotor and for biasing the vanerotor relative to the housing in a specified phase-change directionunder a preload of the torsion spring, adjacent coils of the torsionspring being brought into contact with each other at a part of thetorsion spring in a circumferential direction under a state where thetorsion spring is loaded, and a back-pressure relief passage throughwhich a back-pressure chamber, configured to install the biasing memberof the lock mechanism, is communicated with an exterior space of thehousing, the back-pressure relief passage configured to open toward thetorsion spring, wherein the back-pressure relief passage is provided ata predetermined circumferential position that goes across a coil-to-coilcontact part that the adjacent coils of the torsion spring are broughtinto contact with each other when the vane rotor rotates relative to thehousing by a maximum angular displacement.

According to another aspect of the invention, a valve timing controlapparatus of an internal combustion engine comprises a driving rotarymember adapted to be driven by a crankshaft of the engine, a drivenrotary member adapted to be fixedly connected to a camshaft andconfigured to phase-change relative to the driving rotary member bysupplying or discharging working oil, and also configured to have acylinder structural bore formed to extend in a direction of a rotationaxis of the driven rotary member, a lock mechanism having a lock memberslidably installed in the cylinder structural bore and a biasing memberfor biasing the lock member in its extended direction from the vanerotor, the lock mechanism being configured to permit the lock member tobe displaced in its retracted direction against a biasing force of thebiasing member by hydraulic pressure acting on the lock member, anengaging recess formed in the driving rotary member so as to oppose thelock member, for restricting rotary motion of the driven rotary memberrelative to the driving rotary member by bringing the lock member intoengagement with the engaging recess with sliding motion of the lockmember in the extended direction, a helical torsion spring attached atone end to the driven rotary member and attached at the other end to thedriving rotary member, for exerting a biasing force on the vane rotorand for biasing the vane rotor relative to the housing in a specifiedphase-change direction under a preload of the torsion spring, adjacentcoils of the torsion spring being brought into contact with each otherat a part of the torsion spring in a circumferential direction under astate where the torsion spring is loaded, a spring guide provided tosurround an outer periphery of the torsion spring, and a back-pressurerelief passage through which a back-pressure chamber, configured toinstall the biasing member of the lock mechanism, is communicated withan inner periphery of the spring guide, wherein the back-pressure reliefpassage is provided at a predetermined circumferential position thatgoes across a point of contact between the spring guide and the torsionspring at which the outer periphery of the torsion spring is moststrongly brought into contact with the inner periphery of the springguide when the driven rotary member rotates relative to the drivingrotary member by a maximum angular displacement.

According to a further aspect of the invention, a valve timing controlapparatus of an internal combustion engine comprises a housing adaptedto be driven by a crankshaft of the engine, and configured to define aplurality of working-fluid chambers therein by partitioning an internalspace by a plurality of shoes protruding radially inward from an innerperipheral surface of the housing, a vane rotor having a rotor adaptedto be fixedly connected to a camshaft and a plurality ofradially-extending vanes formed on an outer periphery of the rotor forpartitioning each of the working-fluid chambers of the housing by theshoes and the vanes to define phase-advance working chambers andphase-retard working chambers, the vane rotor being configured tophase-advance relative to the housing by supplying hydraulic pressure toeach of the phase-advance working chambers and by discharging workingoil in each of the phase-retard working chambers and configured tophase-retard relative to the housing by supplying hydraulic pressure toeach of the phase-retard working chambers and by discharging working oilin each of the phase-advance working chambers, and also configured tohave a cylinder structural bore formed in at least one of the pluralityof vanes as a through hole extending in a direction of a rotation axisof the vane rotor, a lock mechanism having a lock member slidablyinstalled in the cylinder structural bore and a biasing member forbiasing the lock member in its extended direction from the vane rotor,the lock mechanism being configured to permit the lock member to bedisplaced in its retracted direction against a biasing force of thebiasing member by hydraulic pressure acting on the lock member, anengaging recess formed in the housing so as to oppose the lock member,for restricting rotary motion of the vane rotor relative to the housingby bringing the lock member into engagement with the engaging recesswith sliding motion of the lock member in the extended direction, ahelical torsion spring attached at one end to the vane rotor andattached at the other end to the housing, for exerting a biasing forceon the vane rotor and for biasing the vane rotor relative to the housingin a specified phase-change direction under a preload of the torsionspring, adjacent coils of the torsion spring being brought into contactwith each other at a part of the torsion spring in a circumferentialdirection under a state where the torsion spring is loaded, and aback-pressure relief passage through which a back-pressure chamber,configured to install the biasing member of the lock mechanism, iscommunicated with an exterior space of the housing, the back-pressurerelief passage configured to open toward the torsion spring, wherein theback-pressure relief passage is provided at a predeterminedcircumferential position that goes across a given angular positiondisplaced from a spring-retainer position at which the other end of thetorsion spring is attached to the housing by approximately 90 degrees ina direction opposite to a spring-loaded direction of the torsion spring.

The other objects and features of this invention will become understoodfrom the following description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a disassembled view illustrating an embodiment of a valvetiming control (VTC) apparatus.

FIG. 2 is a front elevation view illustrating the VTC apparatus of theembodiment.

FIG. 3 shows a longitudinal cross section of the VTC apparatus shown inFIG. 2 and also shows a schematic hydraulic circuit for controlling theVTC apparatus.

FIG. 4 is an explanatory view illustrating the essential part of theinternal structure of the VTC apparatus of FIG. 2, controlled to amaximum phase-advance angular position of a vane rotor relative to ahousing.

FIG. 5 is an explanatory view illustrating the essential part of theinternal structure of the VTC apparatus of FIG. 2, controlled to amaximum phase-retard angular position of the rotor relative to thehousing.

FIG. 6 is an enlarged cross section illustrating the essential part ofthe lock mechanism shown in FIG. 3.

FIG. 7A is a front elevation view illustrating only the helical torsionspring shown in FIG. 3, whereas FIG. 7B is a cross section of thehelical torsion spring, taken along the line A-A of FIG. 7A.

FIG. 8 is an enlarged cross section illustrating the essential part ofthe VTC apparatus shown in FIG. 3 with the helical torsion spring in theassembled state.

FIGS. 9A-9B are explanatory views illustrating assembling processes ofthe helical torsion spring shown in FIG. 3, FIG. 9A showing thedisassembled state of the helical torsion spring, and FIG. 9B showingthe assembled state of the helical torsion spring.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, the valve timing control apparatus of theembodiment is exemplified in a hydraulically-operated rotary vane typevariable valve timing control (VTC) apparatus installed in an internalcombustion engine of an automotive vehicle.

As shown in FIG. 3, the hydraulically-operated rotary vane type VTCapparatus is interleaved between a timing sprocket 1, which sprocket isdriven by an engine crankshaft, and a camshaft 2, whose one axial end isrotatably fitted to a central bore of sprocket 1, such that rotarymotion of camshaft 2 relative to sprocket 1 is permitted. The operationof the VTC apparatus is controlled by means of a hydraulicsupply-and-drain means 4 (described later), for phase-conversion of theangular phase of camshaft 2 relative to sprocket 1.

Concretely, as shown in FIGS. 3-5, the VTC apparatus is mainlyconstructed by a vane rotor 10 and a housing 20 configured toaccommodate the vane rotor 10 in an internal space defined in thehousing 20 such that rotary motion of vane rotor 10 relative to housing20 is permitted. Vane rotor 10 is comprised of a cylindrical rotor body15 fixedly connected to the one axial end of camshaft 2 for co-rotationwith the camshaft 2 and a plurality of vane blades (simply, vanes),radially-outward protruding from the outer periphery of rotor body 15.In the shown embodiment, the plurality of vanes are four vanes 11-14. Asdescribed later, housing 20 is a substantially cylindrical drivingrotary member which is comprised of a front plate 26, a substantiallycylindrical housing body 25, and a rear plate 27 (see FIG. 3). The rearplate 27 of housing 20 is integrally formed with the sprocket 1. Aplurality of radially-inward protruding shoes (four shoes 21-24 in theshown embodiment), associated with respective vanes 11-14 of vane rotor10, are integrally formed on the inner periphery of the housing body 25.Four vanes 11-14 of vane rotor 10 and four shoes 21-24 of housing 20cooperate with each other to define four variable-volume phase-advanceworking chambers (simply, phase-advance chambers) Ad and fourvariable-volume phase-retard working chambers (simply, phase-retardchambers) Re. The operation of the VTC apparatus is controlled bysupplying hydraulic pressure (working oil) selectively to either one ofeach of phase-retard chambers Re and each of phase-advance chambers Advia the hydraulic supply-and-drain means 4.

As shown in FIGS. 1-3, a helical torsion spring 30 is interleavedbetween the vane rotor 10 and the housing 20, such that one end 30 a ofhelical torsion spring 30 is retained or held on the vane rotor 10 andthe other end 30 b of helical torsion spring 30 is retained or held onthe housing 20. With the torsion spring 30 interleaved between the vanerotor 10 and the housing 20 under a preload, vane rotor 10 is forced orbiased in a phase-advance direction (clockwise with respect to thehousing 20, viewing FIGS. 4-5). Torsion spring 30 is configured suchthat a biasing force of torsion spring 30 acts to force or bias the vanerotor 10 in the phase-advance direction against so-called alternatingtorque, transmitted through the camshaft 2 and acting to phase-retardthe camshaft 2 (i.e., the vane rotor 10) relative to the crankshaft(i.e., the housing 20), immediately before the engine is put into astopped state where there is a less hydraulic-pressure supply to each ofphase-advance and phase-retard chambers Ad and Re. By the way, as bestseen from the cross section of FIG. 7B showing one example of thetorsion spring, torsion spring 30 of the shown embodiment is a helicaltorsion spring having a substantially rectangular longitudinal crosssection and made from a flat square wire having a substantiallyrectangular lateral cross section, more precisely, a lateral crosssection of a long side in a radial direction of the helical torsionspring and a short side in an axial direction of the helical torsionspring. By the use of the helical torsion spring made from a flat squarewire, it is possible to reduce the axial length of torsion spring 30.This contributes to the reduced axial dimension of the torsion-springequipped VTC apparatus.

As best seen in FIG. 3, vane rotor 10 has a central cylindrical-hollowfitting groove 15 a formed on the right-hand side facing the one axialend of camshaft 2. Vane rotor 10 is fitted onto the one axial end ofcamshaft 2 via the cylindrical-hollow fitting groove 15 a. Also, vanerotor 10 has an axially-extending central bore 15 b (a through hole)into which a cam bolt (vane mounting bolt) 5 is inserted for bolting thevane rotor 10 to the one axial end of camshaft 2 by axially tighteningthe cam bolt, for co-rotation with the camshaft 2. With thisarrangement, the angular phase of camshaft 2 relative to the crankshaftcan be changed by relatively rotating the vane rotor 10, which rotor isconfigured to rotate in synchronism with rotation of the camshaft 2,with respect to the housing 20, which housing is configured to rotate insynchronism with rotation of the engine crankshaft. This enables theengine valve timing (valve open timing and valve closure timing) to bechanged.

As can be seen in FIGS. 3-5, a plurality of radial communication bores(four radial through holes 16, 16, 16, 16 in the shown embodiment) areformed at predetermined circumferential positions of vane rotor 10 andlocated adjacent to the roots of respective vanes 11-14. The outermostends of radial communication bores 16 are configured to open intorespective phase-advance chambers Ad (see FIGS. 4-5). On the other hand,the innermost ends of radial communication bores 16 are configured tocommunicate with a phase-advance side oil passage 52 (described later)formed in the camshaft 2. Hence, phase-advance chambers Ad are alwayscommunicated with the phase-advance side oil passage 52 throughrespective radial communication bores 16. Thus, hydraulic-pressuresupply to respective phase-advance chambers Ad via the hydraulicsupply-and-drain means 4 and hydraulic-pressure discharge fromrespective phase-advance chambers Ad via the hydraulic supply-and-drainmeans 4 are achieved through the radial communication bores 16 as wellas the phase-advance side oil passage 52.

As shown in Figs.1-5, rotor body 15 of vane rotor 10 has a substantiallyring-shaped flat-faced collar-head-bolt seat 17 formed on the left-handside (viewing FIG. 3) facing the front plate 26 in a manner so as tosurround the axially-extending central bore 15 b of vane rotor 10. Whenassembling, a collar head 5 a of cam bolt 5 is seated on thecollar-head-bolt seat 17. An annularly-grooved torsion-spring seat 18(an annular groove constructing part of a spring guide 41 describedlater) is recessed or formed in the outer periphery of collar-head-boltseat 17. The one end 30 a of torsion spring 30 is seated on theannularly-grooved torsion-spring seat 18. The outside diameter ofcollar-head-bolt seat 17 is set or dimensioned to be slightly less thanthe coil inside diameter of a coiled spring portion 30 c of torsionspring 30, so as to ensure a clearance fit (a loose fit) between theouter periphery of collar-head-bolt seat 17 and the inner periphery ofthe coiled spring portion 30 c. As best seen from the front elevationview of FIG. 2, the circumference of the flat top face ofcollar-head-bolt seat 17 is formed as a rounded edge portion or afrusto-conical chamfered (tapered) edge portion 17 a, machined in thecircumferential direction. This chamfered edge portion 17 a suppresses apart of the coiled spring portion 30 c from being caught on the edge ofthe circumference of collar-head-bolt seat 17 when the torsion spring 30is loaded or twisted so as to cause a deformation of the coiled springportion 30 c in the winding direction, thus ensuring a smooth torsionaldeformation of torsion spring 30.

As clearly shown in FIGS. 1-3, the substantially ring-shaped flat-facedcollar-head-bolt seat 17 has a radially-recessed groove 19 formed ormachined to be continuous with the annularly-grooved torsion-spring seat18 in a manner so as to communicate the central bore 15 b with theannularly-grooved torsion-spring seat 18 through the radially-recessedgroove. The radially-recessed groove 19 serves as a first springretainer that retains or holds the one end 30 a (exactly, aradially-inward bent short arm (hereunder described in detail) of theone spring end 30 a) of torsion spring 30. Concretely, the one end 30 aof torsion spring 30 is bent radially inward from the outer peripheralside of collar-head-bolt seat 17 to the center such that theradially-inward bent short arm of the one spring end 30 a is configuredto be substantially conformable to the shape of the first springretainer 19 (i.e., the radially-recessed groove of collar-head-bolt seat17) and thus the radially-inward bent short arm of the one spring end 30a can be certainly retained in the first spring retainer 19. The collarhead 5 a of cam bolt 5, which bolt is screwed into the front end ofcamshaft 2 through the axially-extending central bore 15 b of vane rotor10, also overlaps with the axial opening end of the first springretainer 19 (i.e., the radially-recessed groove of collar-head-bolt seat17) in a manner so as to close most of the axial opening end (theleft-hand opening end, viewing FIG. 3) of the first spring retainer 19.This prevents the one end 30 a of torsion spring 30 from falling out ofthe first spring retainer 19. The utilization of the existing structure,such as the collar head 5 a of cam bolt 5, eliminates the necessity ofhaving a separate spring retainer for retaining the one end 30 a oftorsion spring 30. This contributes to lower assembling/installationtime and costs and reduced production costs.

As shown in FIGS. 1, and 4-5, each of vanes 11-14 has anaxially-elongated seal groove formed in its apex along the axialdirection of rotor body 15. Four elongated oil seals S1 are fitted intoand retained in the respective seal grooves of vanes 11-14. Bysliding-contact between each of oil seals S1 of vanes 11-14 and theinner peripheral wall surface of the housing body 25, four spaces,defined among four shoes 21-24, are partitioned into four pairs ofphase-advance and phase-retard chambers (Ad, Re), (Ad, Re), (Ad, Re),and (Ad, Re). A given one (hereinafter is referred to as “wide vane”) offour vanes 11-14 is configured as a wide vane having an invertedtrapezoidal shape in lateral cross section, whereas the remaining vanes12-14 are configured to be substantially rectangular in lateral crosssection. The remaining three vanes 12-14 have almost the samecircumferential width and the same radial length. The circumferentialwidth of the wide vane 11 having the inverted trapezoidal shape isdimensioned to be greater than that of each of the remaining vanes12-14. The maximum angular displacement of vane rotor 10 relative tohousing 20 in the phase-advance direction is restricted by abutment ofthe wide vane 11 with the shoe 21 of the two adjacent shoes 21 and 24.Conversely, the maximum angular displacement of vane rotor 10 relativeto housing 20 in the phase-retard direction is restricted by abutment ofthe wide vane 11 with the shoe 24 of the two adjacent shoes 21 and 24.Also, a lock mechanism 31 (interlocking means) is installed in the widevane 11 for holding the angular phase of vane rotor 10 relative tohousing 20 at a given angular-phase position such as a maximumphase-advance position when the engine is shifted to a stopped state.

As shown in FIGS. 3-6, particularly, as best seen from the longitudinalcross section of FIG. 3, lock mechanism 31 is mainly comprised of asubstantially cylindrical lock pin 32 and a return spring (a coiledcompression spring) 33. Lock pin 32 is slidably installed in a lock-pinaccommodation bore, simply, a lock-pin bore 34 (a cylinder structuralbore) formed in the wide vane 11 as an axially-extending stepped throughhole. Lock pin 32 is configured to be substantially conformable to theshape of lock-pin bore 34. By engaging the lock pin 32 with an engaginghole 35 formed in the rear plate 27, constructing a part of housing 20,rotary motion of vane rotor 10 relative to housing 20 can be restricted.Return spring 33 is interleaved between the lock pin 32 and the frontplate 26, constructing a part of housing 20, under preload, forpermanently forcing or biasing the lock pin 32 toward the rear plate 27.

More concretely, as clearly shown in FIG. 6, lock pin 32 is formed as ahollow stepped cylinder that the root (the left-hand side of pin 32,viewing FIG. 6) is formed as a large-diameter portion 32 a and the other(the right-hand side of pin 32) is formed as a small-diameter portion 32b. In a similar manner, lock-pin bore 34 is formed as a stepped throughhole that the left-hand half (viewing FIG. 6) is formed as alarge-diameter bore 34 a and the right-hand half is formed as asmall-diameter bore 34 b. When assembling, the large-diameter portion 32a of lock pin 32 is kept in sliding-contact with the large-diameter bore34 a of lock-pin bore 34, whereas the small-diameter portion 32 b oflock pin 32 is kept in sliding-contact with the small-diameter bore 34 bof lock-pin bore 34. A back-pressure chamber 36 is defined by thelarge-diameter portion 32 a in sliding-contact with the large-diameterbore 34 a. Return spring 33 is elastically installed into aspring-retainer bore formed in the lock pin 32 through the back-pressurechamber 36. By the way, hydraulic pressure in the phase-retard chamberRe, defined between the wide vane 11 and the shoe 21, is supplied intothe engaging hole 35 of the rear plate 27 through a recessedcommunication groove 37 (see FIGS. 1 and 4-5, in particular, see FIG. 1)formed in the right-hand sidewall (viewing FIG. 1) of the wide vane 11,facing the rear plate 27. Hence, the lock mechanism is configured sothat the lock pin 32 can be brought into and out of engagement with theengaging hole 35 depending on the hydraulic pressure in the phase-retardchamber Re.

Also, as seen from the enlarged cross section of FIG. 6, an annularspace 38 is defined between the stepped portion 32 c (formed between thelarge-diameter portion 32 a and the small-diameter portion 32 b of lockpin 32) and the stepped portion 34 c (formed between the large-diameterbore 34 a and the small-diameter bore 34 b of lock-pin bore 34). Theannular space 38 is configured to communicate with the phase-advancechamber Ad, defined between the wide vane 11 and the shoe 24, through athrough hole 39 (see FIGS. 4-5 and 6, in particular, see FIG. 6) formedin the wide vane 11 in a manner so as to extend from the lock-pin bore34 to this phase-advance chamber Ad. That is, the hydraulic pressure inthe phase-advance chamber Ad is always introduced or supplied via thethrough hole 39 into the annular space 38. When the hydraulic pressurein the phase-advance chamber Ad exceeds a predetermined high-pressurelevel, a lock-pin disengagement state where the lock pin 32 is out ofengagement with the engaging hole 35 can be maintained.

As clearly shown in FIGS. 1, 3-6, and 8, a recessed communication groove40 a is formed in the left-hand sidewall (viewing FIG. 1) of the widevane 11, facing the front plate 26, for communicating the lock-pin bore34 with the annularly-grooved torsion-spring seat 18 through therecessed communication groove 40 a. That is, the axial opening end (theleft-hand opening end, viewing FIGS. 3 and 6) of the recessedcommunication groove 40 a is closed by the front plate 26 to define aback-pressure relief passage 40 for discharging or relieving workingoil, leaked from the annular space 38 into the back-pressure chamber 36through a very small radial clearance space defined between the outerperipheral surface of the large-diameter portion 32 a of lock pin 32 andthe inner peripheral surface of the large-diameter bore 34 a of lock-pinbore 34, toward the side of annularly-grooved torsion-spring seat 18.Notice that the back-pressure relief passage 40 (i.e., the recessedcommunication groove 40 a) is configured or formed at a predeterminedcircumferential position that the back-pressure relief passage 40 (i.e.,the recessed communication groove 40 a) goes across a coil-to-coilcontact part “T” (see FIG. 8) of the coiled spring portion 30 c oftorsion spring 30, that has a narrower coil-to-coil distance and thatthe adjacent coils are brought into contact with each other, when thevane rotor 10 rotates relative to the housing 20 by a maximum angulardisplacement from one of the maximum phase-advance angular position andthe maximum phase-retard angular position to the other. This permitsworking oil, leaked into the back-pressure chamber 36 and discharged byway of the back-pressure relief passage 40 (i.e., the recessedcommunication groove 40 a), to be discharged or directed toward thecoil-to-coil contact part “T”. More concretely, the previously-notedpredetermined circumferential position, going across the coil-to-coilcontact part “T”, corresponds to a circumferential position that goesacross a given angular position displaced from a spring-retainerposition (an angular position of a second spring retainer 45 describedlater), at which the radially-outward bent short arm of the other end 30b of torsion spring 30 is retained, by approximately 90 degrees in thedirection (i.e., the load-released direction) opposite to the twistdirection (i.e., the spring-loaded direction) of torsion spring 30. Onthe assumption that the housing 20 (sprocket 1) is actually rotatingduring operation of the engine but the housing 20 is stationary, theload-released direction of torsion spring 30 corresponds to theclockwise direction in FIGS. 4-5, whereas the spring-loaded direction oftorsion spring 30 corresponds to the counterclockwise direction in FIGS.4-5. This is based on the fact that a twisting force, acting on torsionspring 30, causes the deformed torsion spring to be inclined withrespect to the axis of torsion spring 30 about the other end 30 bforming the fulcrum or the pivot, and hence owing to the twisting force,the given angular position displaced from a spring-retainer position, atwhich the radially-outward bent short arm of the other end 30 b isretained, by approximately 90 degrees in the direction opposite to thetwist direction (i.e., the spring-loaded direction) of torsion spring 30becomes the previously-discussed coil-to-coil contact part “T”.

By the way, regarding the layout of back-pressure relief passage 40, itis more preferable that the back-pressure relief passage 40 is laid outat a predetermined circumferential position going across a press-contactpart “P” (described later by reference to the enlarged cross section ofFIG. 8) that the outer periphery of the coiled spring portion 30 c ismost strongly brought into press-contact with the inner periphery of aspring guide 41 (described later) with contact pressure due to aninclination of the coiled spring portion 30 c with respect to the axis(the centerline) of the torsion spring, when the vane rotor 10 rotatesrelative to the housing 20 by a maximum angular displacement from one ofthe maximum phase-advance angular position and the maximum phase-retardangular position to the other. With the more preferable layout ofback-pressure relief passage 40, working oil, leaked into theback-pressure chamber 36 and discharged by way of the back-pressurerelief passage 40 (i.e., the recessed communication groove 40 a) can bedirected toward the press-contact part “P” of the coiled spring portion30 c with the spring guide 41 as well as the coil-to-coil contact part“T” of the coiled spring portion 30 c.

As shown in FIGS. 1-5, particularly, as best seen from the longitudinalcross section of FIG. 3, housing 20 is comprised of the substantiallycylindrical-hollow housing body 25, the front plate 26, and the rearplate 27. As previously noted, housing body 25 has four radially-inwardprotruding shoes 21-24 integrally formed on the inner periphery. Frontplate 26 is configured to close the front opening end of the housingbody 25, whereas rear plate 27 is configured to close the rear openingend of the housing body 25. Housing body 25 and front and rear plates26-27 are axially fastened together and integrally connected to eachother with four bolts 6.

In a similar manner to the four oil seals S1 fitted into the respectiveseal grooves of shoes 11-14, as shown in FIGS. 1, and 4-5, each of shoes21-24 has an axially-elongated seal groove formed in its apex along theaxial direction of vane rotor 10. Four elongated oil seals S2 are fittedinto and retained in the respective seal grooves of shoes 21-24. Bysliding-contact between each of oil seals S1 of vanes 11-14 and theinner peripheral wall surface of the housing body 25 and bysliding-contact between each of oil seals S2 of shoes 21-24 and theouter peripheral wall surface of the rotor body 15, four spaces, definedamong four shoes 21-24, are partitioned into four pairs of phase-advanceand phase-retard chambers (Ad, Re), (Ad, Re), (Ad, Re), and (Ad, Re).Additionally, regarding a pair of shoes 21 and 24, located adjacent tothe wide vane 11, as clearly shown in FIGS. 4-5, each of shoes 21 and 24is integrally formed at its root with a circumferentially-protruding,partially thick-walled portion 28, such that the partially thick-wallportion 28 of shoe 21 and the partially thick-walled portion 28 of shoe24 are circumferentially opposed to each other. When the vane rotor 10is displaced relative to the housing 20 in the phase-advance direction,the partially thick-wall portion 28 of shoe 21 functions to restrict themaximum angular displacement in the phase-advance direction by abutmentwith the wide vane 11, while ensuring the phase-retard chamber Rebetween the wide vane 11 and the shoe 21. Conversely when the vane rotor10 is displaced relative to the housing 20 in the phase-retarddirection, the partially thick-wall portion 28 of shoe 24 functions torestrict the maximum angular displacement in the phase-retard directionby abutment with the wide vane 11, while ensuring the phase-advancechamber Ad between the wide vane 11 and the shoe 24.

As shown in FIGS. 1-3, front plate 26 is formed as a comparativelythin-walled disc. Front plate 26 has an axially-forward-protrudingcentral cylindrical portion 43 (constructing part of the spring guide 41described later). Cam bolt 5 and torsion spring 30 can be installedthrough a central through hole 43 a of cylindrical portion 43 of frontplate 26 from the outside (see FIGS. 9A-9B). By the way, as best seenfrom the enlarged cross section of FIG. 8, the inside diameter of thecentral through hole 43 a of cylindrical portion 43 of front plate 26 isset or dimensioned to be approximately equal to the inside diameter ofthe radially-outside circumferentially-extending curved peripheral wallsurface of annularly-grooved torsion-spring seat 18 of vane rotor 10such that the central through hole 43 a of cylindrical portion 43 isconfigured to be continuous with the radially-outsidecircumferentially-extending curved peripheral wall surface ofannularly-grooved torsion-spring seat 18. That is, the inner peripheralwall of cylindrical portion 43 of front plate 26 together with thecurved peripheral wall of annularly-grooved torsion-spring seat 18 ofvane rotor 10 is formed as a continuous smooth curved peripheral wallthat constructs the spring guide 41 for torsion spring 30. The internalspace, defined in the spring guide 41 (i.e., the curved peripheral wallof annularly-grooved torsion-spring seat 18 of vane rotor 10 and theinner peripheral wall of central through hole 43 a of front plate 26),serves as a spring accommodation bore 42 (a torsion spring chamber) inwhich the coiled spring portion 30 c of torsion spring 30 isaccommodated. With the previously-discussed arrangement, the coiledspring portion 30 c of torsion spring 30 can be installed in the springaccommodation bore 42 in a manner so as to enable or permit smoothtorsional motion of torsion spring 30 in both directions of winding andunwinding. This ensures smooth deformation of the coiled spring portion30 c during application of torque to the torsion spring 30.

As clearly shown in FIGS. 1-2, a substantially ring-shapedaxially-forward-protruding end 43 b of cylindrical portion 43 has acutout 44 partially cut out in its circumferential direction. The rootof one sidewall 44 a of circumferentially-opposed sidewalls 44 a-44 b ofcutout 44, is further cut out partially in the circumferential directionso as to form a radially-cutout groove. The further radially-cutoutgroove 45 serves as a second spring retainer that retains or holds theother end 30 b (exactly, a radially-outward bent short arm (hereunderdescribed in detail) of the other spring end 30 b) of torsion spring 30.Concretely, the other end 30 b of torsion spring 30 is bent radiallyoutward, such that the radially-outward bent short arm of the otherspring end 30 b is configured to be substantially conformable to theshape of the second spring retainer 45 (i.e., the furtherradially-cutout groove of cutout 44 of cylindrical portion 43 of frontplate 26) and thus the radially-outward bent short arm of the otherspring end 30 b can be certainly retained in the second spring retainer45. In this manner, by constructing or machining the second springretainer 45 in the form of the further radially-cutout groove configuredto open at the ring-shaped axially-forward-protruding end 43 b ofcylindrical portion 43, as can be seen from the explanatory views ofFIGS. 9A-9B, it is possible to easily assemble or install the torsionspring 30 on the annularly-grooved torsion-spring seat 18 of rotor body15 through the central through hole 43 a of cylindrical portion 43 offront plate 26 from the outside. As a result of this, it is possible toavoid a complicated assembling work that other component parts areinstalled, while relatively rotating the vane rotor 10 with respect tothe housing 20 against the biasing force of torsion spring 30 after thetorsion spring 30 has been installed. This contributes to the goodproductivity of the torsion-spring equipped VTC apparatus. In the shownembodiment, as best seen in FIG. 2, the circumferentially-opposedsidewalls 44 a-44 b of cutout 44 are configured to be substantiallyparallel with each other. In order for a straight line “L1”, obtained byradially inwardly extending the end face 45 a of the second springretainer 45 (i.e., the further radially-cutout groove of cutout 44),which end face is configured to face in the circumferential directionand at which the radially-outward bent short arm of the other end 30 bof torsion spring 30 is retained, to pass through the vicinity of thecenter “C” of cylindrical portion 43 of front plate 26, the straightline “L1” is arranged in close proximity to the center “C” ofcylindrical portion 43, rather than a straight line “L2”, obtained byradially inwardly extending the other sidewall 44 b ofcircumferentially-opposed sidewalls 44 a-44 b of cutout 44. Moreconcretely, the cutout 44 is radially pierced or cut and formed with apunching tool at a given position at which the end face 45 a of thesecond spring retainer 45 is offset toward a straight line “L0” passingthrough the center “C” of cylindrical portion 43 relatively to the othersidewall 44 b of cutout 44. The cutout 44 is configured such that theangle “θ” between the other sidewall 44 b and a tangential line “L3” atthe intersection point “X” of the other sidewall 44 b and the innerperipheral wall surface of cylindrical portion 43 is an obtuse angle.

Additionally, the second spring retainer 45 is configured as theradially-cutout groove formed or machined by further cutting outpartially only the root of the one sidewall 44 a of cutout 44. Hence,the circumferential width “W1” of the cutout 44 at the tip of thering-shaped axially-forward-protruding end 43 b is dimensioned to benarrower than the circumferential width “W2” of the cutout 44 at theroot of the ring-shaped axially-forward-protruding end 43 b. The insideface 45 b of the second spring retainer 45, which inside face isconfigured to face in the axial direction, functions as a fall-outprevention spring short-arm retainer for restricting axial movement ofthe other end 30 b of torsion spring 30 and for retaining theradially-outward bent short arm of the other end 30 b in place. By meansof the fall-out prevention spring short-arm retainer 45 b, it ispossible to restrict or suppress the torsion spring 30 from falling out,thus stably retaining the torsion spring in place.

As shown in FIGS. 1 and 3-5, rear plate 27 is formed as a comparativelythick-wall disc. Rear plate 27 is integrally formed at its outerperiphery with the sprocket 1. As best seen in FIG. 1, rear plate 27 hasa central through hole 27 a into which the front end of camshaft 2 isinserted. Also, rear plate 27 has fourcircumferentially-equidistant-spaced female-screw threaded portions 27 bin to which respective bolts 6 are screwed. Furthermore, a plurality ofradial communication grooves (four radial communication grooves 46, 46,46, 46 in the shown embodiment) are formed in the inside face of rearplate 27 and arranged to be cut out at predetermined circumferentialpositions of rear plate 27 and located along the peripheral edge ofcentral through hole 27 a. The outermost ends of radial communicationgrooves 46 are configured to open into respective phase-retard chambersRe (see FIGS. 4-5). On the other hand, the innermost ends of radialcommunication grooves 46 are configured to communicate with aphase-retard side oil passage 51 (described later) formed in thecamshaft 2. Hence, phase-retard chambers Re are always communicated withthe phase-retard side oil passage 51 through respective radialcommunication grooves 46. Thus, hydraulic-pressure supply to respectivephase-retard chambers Re via the hydraulic supply-and-drain means 4 andhydraulic-pressure discharge from respective phase-retard chambers Revia the hydraulic supply-and-drain means 4 are achieved through theradial communication grooves 46 as well as the phase-retard side oilpassage 51.

Additionally, as described previously, rear plate 27 has the engaginghole 35 (see FIGS. 1, 3, and 6) formed in the inside face of rear plate27 and brought into engagement with the lock pin 32 slidably installedin the lock-pin bore 34 of vane rotor 10 when vane rotor 10 ispositioned at its maximum phase-advance position (see FIG. 4), so as torestrict rotary motion of vane rotor 10 relative to housing 20. As seenfrom the enlarged cross section of FIG. 6, engaging hole 35 is formed asa comparatively shallow stepped recessed groove that the left-hand half(viewing FIG. 6) is formed as a large-diameter circular recessed groove35 a and the right-hand half (viewing FIG. 6) is formed as asmall-diameter circular recessed groove 35 b. The inside diameter oflarge-diameter circular recessed groove 35 a is dimensioned to begreater than the outside diameter of small-diameter portion 32 b of lockpin 32. On the other hand, the inside diameter of small-diametercircular recessed groove 35 b (the bottom groove) is dimensioned to beless than the outside diameter of small-diameter portion 32 b of lockpin 32. When the angular phase of vane rotor 10 relative to housing 20has been held at the maximum phase-advance state (see FIG. 4), rotarymotion of vane rotor 10 relative to housing 20 can be restricted byengagement of the lock pin 32 with the large-diameter circular recessedgroove 35 a.

Moreover, as clearly shown in FIGS. 1, and 4-5, rear plate 27 has anaxially-protruding positioning pin 48 formed on the inside face of rearplate 27. On the other hand, housing body 25 has an axially-elongatedengaging groove 47 cut in the outer periphery of housing body 25.Engaging the positioning pin 48 of rear plate 27 with the engaginggroove 47 of housing body 25, ensures the proper positioning of the rearplate 27 on the housing body 25. The provision of the positioning pin 48ensures a good engagement relationship of the lock pin 32 with theengaging hole 35 after three housing members, namely housing body 25,and front and rear plates 26-27 have been assembled each other andintegrally connected to each other with four bolts 6.

As shown in FIG. 3, hydraulic supply-and-drain means 4 is provided forselectively supplying and draining hydraulic pressure (working oil) toand from either one of each phase-advance chamber Ad and eachphase-retard chamber Re. Hydraulic supply-and-drain means 4 is mainlycomprised of the phase-retard side oil passage 51 connected to each ofradial communication grooves 46, the phase-advance side oil passage 52connected to each of radial communication bores 16, an oil pump 53, anda drain passage 54. Oil pump 53 serves as a hydraulic pressure sourcefor supplying hydraulic pressure (working oil) to a selected one of theoil passages 51-52 through the use of a generally-known electromagneticsolenoid-operated directional control valve 55. Drain passage 54 isconfigured for draining or directing hydraulic pressure (working oil)from the unselected oil passage of the oil passages 51-52 through theuse of the electromagnetic directional control valve 55 to an oil pan56. By the way, electromagnetic directional control valve 55 of theshown embodiment is a so-called three-position, spring-offset, four-waysolenoid-operated directional control valve. Electromagnetic directionalcontrol valve 55 uses a sliding spool to change the path of flow throughthe directional control valve. As seen from the hydraulic circuitdiagram of FIG. 3, for a given position of the spool, a unique flow pathconfiguration exists within the directional control valve. Directionalcontrol valve 55 is designed to operate with either three positions ofthe spool. The flow path configuration for each unique spool positioncan be controlled responsively to a control signal from an electroniccontrol unit ECU (not shown).

The operation and effects of the VTC apparatus of the internalcombustion engine of the embodiment are hereunder described in detail inreference to FIGS. 3-5.

During an engine startup, as shown in FIGS. 3-4, vane rotor 10 is heldat the given angular-phase position (i.e., the maximum phase-advanceposition) suited to the engine startup by engagement of the tip ofsmall-diameter portion 32 b of lock pin 32 with the large-diametercircular recessed groove 35 a of engaging hole 35, thus ensuring smoothcranking operation, that is, better startup, immediately when anignition switch (not shown) is turned ON.

During operation of the engine in a first predetermined load range afterthe engine has been started up, directional control valve 55 becomesenergized (ON) responsively to a control signal from the ECU. Hence,fluid-communication between the phase-retard side oil passage 51 and theoil pump 53 becomes established and simultaneously fluid-communicationbetween the phase-advance side oil passage 52 and the drain passage 54becomes established. That is, working oil, discharged from the oil pump53, is flown into each of phase-retard chambers Re through thephase-retard side oil passage 51, and thus hydraulic pressure in each ofphase-retard chambers Re becomes high. At this time, working oil in eachof phase-advance chambers Ad is directed through the phase-advance sideoil passage 52 and the drain passage 54 to the oil pan 56, and thushydraulic pressure in each of phase-advance chambers Ad becomes low. Bythe way, part of working oil, flown into the phase-retard chamber Re,defined between the wide vane 11 and the shoe 21, is further flown orsupplied into the engaging hole 35. Hence, the lock pin 32 is broughtout of engagement with the engaging hole 135, thereby permitting freerotary motion of vane rotor 10 relative to housing 20. As a result,owing to an increase in the volume of each phase-retard chamber Re,arising from hydraulic-pressure supply (working-oil supply) to eachphase-retard chamber Re, vane rotor 10 rotates counterclockwise andtherefore the angular phase of camshaft 2 relative to the crankshaft isconverted to a phase-retard side (see FIG. 5).

In contrast, when the engine operating condition has been shifted to asecond predetermined load range, directional control valve 55 becomesde-energized (OFF) responsively to a control signal from the ECU. Hence,fluid-communication between the phase-advance side oil passage 52 andthe oil pump 53 becomes established and simultaneouslyfluid-communication between the phase-retard side oil passage 51 and thedrain passage 54 becomes established. That is, working oil in each ofphase-retard chambers Re is directed through the phase-retard side oilpassage 51 and the drain passage 54 to the oil pan 56, and thushydraulic pressure in each of phase-retard chambers Re becomes low. Atthis time, working oil, discharged from the oil pump 53, is flown intoeach of phase-advance chambers Ad through the phase-advance side oilpassage 52, and thus hydraulic pressure in each of phase-advancechambers Ad becomes high. Owing to hydraulic-pressure supply to eachphase-advance chamber Ad, there is an increased tendency for thehydraulic pressure in the phase-advance chamber Ad, defined between thewide vane 11 and the shoe 24, to be positively supplied via the throughhole 39 into the annular space 38. With the hydraulic pressure suppliedto the annular space 38 and exceeding the predetermined high-pressurelevel, the lock-pin disengagement state where the lock pin 32 is out ofengagement with the engaging hole 35 can be maintained. As a result,owing to an increase in the volume of each phase-advance chamber Ad,arising from hydraulic-pressure supply (working-oil supply) to eachphase-advance chamber Ad, vane rotor 10 rotates clockwise and thereforethe angular phase of camshaft 2 relative to the crankshaft is convertedto a phase-advance side (see FIG. 4).

Immediately before the engine becomes put into a stopped state,hydraulic-pressure supply to each of phase-advance and phase-retardchambers Ad-Re becomes stopped, and hence there is an increased tendencyfor the angular phase of vane rotor 10 relative to housing 20 to beshifted to the phase-retard side by alternating torque acting on thecamshaft 2. However, by virtue of the biasing force (i.e., the opposingtorque) of torsion spring 30, interleaved between the vane rotor 10 andthe housing 20, as shown in FIG. 4, the vane rotor 10 rotates relativeto the housing 20 toward the phase-advance side against the alternatingtorque (the torque applied from the valve springs via the camshaft tothe vane rotor), and then the tip of small-diameter portion 32 h of lockpin 32 is brought into engagement with the large-diameter circularrecessed groove 35 a of engaging hole 35 by the spring force of returnspring 33. Hence, vane rotor 10 is held again at the given angular-phaseposition (i.e., the maximum phase-advance position).

As discussed above, in the VTC apparatus of the embodiment, free rotarymotion of vane rotor 10 relative to housing 20 can be ensured ormaintained by introducing or supplying hydraulic pressure to thelock-pin engaging hole 35 or to the annular space 38. At the same time,working oil, supplied to the engaging hole 35 or to the annular space38, is considerably flown or leaked into the back-pressure chamber 36through the very small radial clearance space defined between the outerperipheral surface of the large-diameter portion 32 a of lock pin 32 andthe inner peripheral surface of the large-diameter bore 34 a of lock-pinbore 34, and then the working oil, flown or leaked into theback-pressure chamber 36, is discharged through the back-pressure reliefpassage 40 (i.e., the recessed communication groove 40 a) into thespring accommodation bore 42.

By the way, as described previously, the back-pressure relief passage 40is configured or formed at a predetermined circumferential position thatthe back-pressure relief passage 40 goes across the coil-to-coil contactpart “T” of the coiled spring portion 30 c of helical torsion spring 30.Hence, working oil, discharged through the back-pressure relief passage40, is directed to the coil-to-coil contact part “T”, thereby enablingthe coil-to-coil contact part “T” of torsion spring 30 to get a properamount of lubrication, and consequently suppressing undesirable wear ofthe coil-to-coil contact part “T”. In particular, in the case of theembodiment using a helical torsion spring having a substantiallyrectangular longitudinal cross section and made from a flat square wire,when torsion spring 30 is loaded or twisted due to the applied torqueand thus a twisted deformation of torsion spring 30 having thesubstantially rectangular longitudinal cross section takes place, thetwisted, deformed torsion spring tends to easily incline in the axialdirection. Hence, in the case of the use of such a helical torsionspring having a substantially rectangular longitudinal cross section,there is an increased tendency for an undesirable coil-to-coil contactto occur, during operation of the VTC apparatus. For the reasonsdiscussed above, the proper amount of lubrication of the coil-to-coilcontact part “T” is effective in smooth, low-friction torsional motionof torsion spring 30. By the way, in the case of the embodiment using ahelical torsion spring made from a flat square wire having a lateralcross section of a long side in the radial direction, when subjected totorque, the twisted, deformed torsion spring tends to more easilyincline in the axial direction, and thus there is a further increasedtendency for an undesirable coil-to-coil contact to occur, duringoperation of the VTC apparatus. Hence, the proper amount of lubricationof the coil-to-coil contact part “T” is more effective in smooth,low-friction torsional motion of torsion spring 30 during operation ofthe VTC apparatus.

In addition to the above, due to the inclination of the coiled springportion 30 c, occurring when subjected to torque, the outer periphery ofthe coil-to-coil contact part “T” is most strongly brought intopress-contact with the inner peripheral surface of the spring guide 41(i.e., the curved peripheral wall of annularly-grooved torsion-springseat 18 of vane rotor 10 and the inner peripheral wall of centralthrough hole 43 a of front plate 26) with contact pressure. Theback-pressure relief passage 40 (i.e., the recessed communication groove40 a) is configured to open through the inner peripheral wall surface ofspring guide 41 into the spring accommodation bore 42. Hence, workingoil, discharged through the back-pressure relief passage 40, is alsodirected to the press-contact part “P”, thereby enabling thepress-contact part “P” of torsion spring 30 to get a proper amount oflubrication, and consequently suppressing undesirable wear and scoringof the press-contact part “P”. That is to say, the proper amount oflubrication of the press-contact part “P” is effective in smooth,low-friction sliding-motion of torsion spring 30 relative to the innerperiphery of spring guide 41 during operation of the VTC apparatus.

As will be appreciated from the above, according to the torsion-springequipped VTC apparatus of the internal combustion engine of theembodiment, the back-pressure relief passage 40 is provided at apredetermined circumferential position going across a circumferentialportion of the coiled spring portion 30 c of torsion spring 30 that (i)the previously-discussed coil-to-coil contact between the adjacent coils(the adjacent turns of wire) and/or (ii) the previously-discussedpress-contact of the outer periphery of the coiled spring portion 30 cwith the inner periphery of the spring guide 41 with contact pressureoccurs due to an inclination of the coiled spring portion 30 c whensubjected to torque during rotary motion of vane rotor 10 relative tohousing 20. More concretely, the previously-noted predeterminedcircumferential position, going across the coil-to-coil contact part “T”and/or the press-contact part “P”, corresponds to a circumferentialposition that goes across a given angular position displaced from theangular position of the second spring retainer 45, at which theradially-outward bent short arm of the other end 30 b of torsion spring30 is retained, by approximately 90 degrees in the direction opposite tothe spring-loaded direction of torsion spring 30. By virtue of workingoil, introduced into the back-pressure relief passage 40, and thendirected to the coil-to-coil contact part “T” and/or the press-contactpart “P”, the coil-to-coil contact part “T” and the press-contact part“P” can be properly lubricated. As a result, it is possible toeffectively suppress undesirable wear, occurring at the coil-to-coilcontact part “T” and/or the press-contact part “P” of the coiled springportion 30 c due to friction.

In the shown embodiment, back-pressure relief passage 40 is constructedby the recessed communication groove 40 a formed in the sliding-contactsurface of the wide vane 11 of vane rotor 10, in sliding-contact withthe inside face of front plate 26. In lieu thereof, back-pressure reliefpassage 40 may be constructed as a radial through hole formed in thewide vane 11 in a manner so as to communicate the back-pressure chamber36 with the spring accommodation bore 42. As compared to theback-pressure relief passage 40, constructed as a radial through holeformed in the wide vane 11, the back-pressure relief passage 40,constructed by the recessed communication passage 40 a, is superior ineasier machining, in other words, good productivity of thetorsion-spring equipped VTC apparatus.

By the way, for the purpose of introducing working oil (lubricating oil)into the spring accommodation bore 42 through the use of theback-pressure relief passage 40, the torsion-spring equipped VTCapparatus of the embodiment adopts a specific clearance-space fluid-flowpath configuration that, first of all, working oil is introduced intothe annular space 38 adjacent to the back-pressure chamber 36, and thenthe introduced working oil is leaked from the annular space 38 throughthe very small radial clearance space defined between the lock pin 32and the lock-pin bore 34 into the back-pressure chamber 36. The annularspace 30 adjacent to the back-pressure chamber 36 functions to properlypromote working-oil leakage through the very small radial clearancespace into the back-pressure chamber 36. This ensures an adequate amountof working oil (lubricating oil) to be supplied through theback-pressure relief passage 40 to the spring accommodation chamber 42,thus enabling the coil-to-coil contact part “T” and/or the press-contactpart “P” to get a proper amount of lubrication.

Furthermore, back-pressure relief passage 40 is positioned on thephase-advance side with respect to an circumferential position (anangular position) of the coil-to-coil contact part “T” of the coiledspring portion 30 c of torsion spring 30 under a locked state where thelock pin 32 of lock mechanism 31 is kept in locked-engagement with thelock-pin bore 34 for restricting rotary motion of vane rotor 10 relativeto housing 20. This ensures more certain lubrication of the coil-to-coilcontact part “T”, during operation of the VTC apparatus.

The entire contents of Japanese Patent Application Nos. 2012-179732(filed Aug. 14, 2012) and 2013-091054 (filed Apr. 24, 2013) areincorporated herein by reference.

While the foregoing is a description of the preferred embodimentscarried out the invention, it will be understood that the invention isnot limited to the particular embodiments shown and described herein,but that various changes and modifications may be made without departingfrom the scope or spirit of this invention as defined by the followingclaims.

What is claimed is:
 1. A valve timing control apparatus of an internalcombustion engine comprising: a housing adapted to be driven by acrankshaft of the engine, and configured to define a plurality ofworking-fluid chambers therein by partitioning an internal space by aplurality of shoes protruding radially inward from an inner peripheralsurface of the housing; a vane rotor having a rotor adapted to befixedly connected to a camshaft and a plurality of radially-extendingvanes formed on an outer periphery of the rotor for partitioning each ofthe working-fluid chambers of the housing by the shoes and the vanes todefine phase-advance working chambers and phase-retard working chambers,the vane rotor being configured to phase-advance relative to the housingby supplying hydraulic pressure to each of the phase-advance workingchambers and by discharging working oil in each of the phase-retardworking chambers and configured to phase-retard relative to the housingby supplying hydraulic pressure to each of the phase-retard workingchambers and by discharging working oil in each of the phase-advanceworking chambers, and also configured to have a cylinder structural boreformed in at least one of the plurality of vanes as a through holeextending in a direction of a rotation axis of the vane rotor; a lockmechanism having a lock member slidably installed in the cylinderstructural bore and a biasing member for biasing the lock member in itsextended direction from the vane rotor, the lock mechanism beingconfigured to permit the lock member to be displaced in its retracteddirection against a biasing force of the biasing member by hydraulicpressure acting on the lock member; an engaging recess formed in thehousing so as to oppose the lock member, for restricting rotary motionof the vane rotor relative to the housing by bringing the lock memberinto engagement with the engaging recess with sliding motion of the lockmember in the extended direction; a helical torsion spring attached atone end to the vane rotor and attached at the other end to the housing,for exerting a biasing force on the vane rotor and for biasing the vanerotor relative to the housing in a specified phase-change directionunder a preload of the torsion spring, adjacent coils of the torsionspring being brought into contact with each other at a part of thetorsion spring in a circumferential direction under a state where thetorsion spring is loaded; and a back-pressure relief passage throughwhich a back-pressure chamber, configured to install the biasing memberof the lock mechanism, is communicated with an exterior space of thehousing, the back-pressure relief passage configured to open toward thetorsion spring, wherein the back-pressure relief passage is provided ata predetermined circumferential position that goes across a coil-to-coilcontact part that the adjacent coils of the torsion spring are broughtinto contact with each other when the vane rotor rotates relative to thehousing by a maximum angular displacement.
 2. The valve timing controlapparatus as claimed in claim 1, further comprising: a spring guideprovided to surround an outer periphery of the torsion spring.
 3. Thevalve timing control apparatus as claimed in claim 2, wherein: thehousing comprises: a cylindrical housing body formed integral with theplurality of shoes protruding radially inward from the inner peripheralsurface of the cylindrical housing body; a front plate configured toclose one axial end of the housing body; and a rear plate configured toclose the other axial end of the housing body, facing the camshaft; thespring guide comprises: an axially-protruding cylindrical portion formedintegral with the front plate; and an annular groove recessed in thevane rotor.
 4. The valve timing control apparatus as claimed in claim 1,wherein: the vane rotor has the back-pressure relief passage, which is arecessed groove formed in a sliding-contact surface of the vane rotor insliding-contact with the front plate.
 5. The valve timing controlapparatus as claimed in claim 1, wherein: the torsion spring is madefrom a flat square wire having a substantially rectangular lateral crosssection.
 6. The valve timing control apparatus as claimed in claim 5,wherein: the torsion spring is made from the flat square wire having thelateral cross section of a longer side in a radial direction of thetorsion spring.
 7. The valve timing control apparatus as claimed inclaim 1, wherein: the back-pressure relief passage is positioned on aphase-advance side with respect to the coil-to-coil contact part of thetorsion spring under a locked state where the lock member of the lockmechanism has been engaged with the engaging recess.
 8. The valve timingcontrol apparatus as claimed in claim 1, wherein: the lock member is astepped lock pin having a stepped portion formed between alarge-diameter portion and a small-diameter portion; and the lockmechanism is configured so that hydraulic pressure acts on at least thestepped portion.
 9. The valve timing control apparatus as claimed inclaim 8, wherein: two hydraulic pressures act on the large-diameterportion and the small-diameter portion separately from each other.
 10. Avalve timing control apparatus of an internal combustion enginecomprising: a driving rotary member adapted to be driven by a crankshaftof the engine; a driven rotary member adapted to be fixedly connected toa camshaft and configured to phase-change relative to the driving rotarymember by supplying or discharging working oil, and also configured tohave a cylinder structural bore formed to extend in a direction of arotation axis of the driven rotary member; a lock mechanism having alock member slidably installed in the cylinder structural bore and abiasing member for biasing the lock member in its extended directionfrom the vane rotor, the lock mechanism being configured to permit thelock member to be displaced in its retracted direction against a biasingforce of the biasing member by hydraulic pressure acting on the lockmember; an engaging recess formed in the driving rotary member so as tooppose the lock member, for restricting rotary motion of the drivenrotary member relative to the driving rotary member by bringing the lockmember into engagement with the engaging recess with sliding motion ofthe lock member in the extended direction; a helical torsion springattached at one end to the driven rotary member and attached at theother end to the driving rotary member, for exerting a biasing force onthe vane rotor and for biasing the vane rotor relative to the housing ina specified phase-change direction under a preload of the torsionspring, adjacent coils of the torsion spring being brought into contactwith each other at a part of the torsion spring in a circumferentialdirection under a state where the torsion spring is loaded; a springguide provided to surround an outer periphery of the torsion spring; anda back-pressure relief passage through which a back-pressure chamber,configured to install the biasing member of the lock mechanism, iscommunicated with an inner periphery of the spring guide, wherein theback-pressure relief passage is provided at a predeterminedcircumferential position that goes across a point of contact between thespring guide and the torsion spring at which the outer periphery of thetorsion spring is most strongly brought into contact with the innerperiphery of the spring guide when the driven rotary member rotatesrelative to the driving rotary member by a maximum angular displacement.11. A valve timing control apparatus of an internal combustion enginecomprising: a housing adapted to be driven by a crankshaft of theengine, and configured to define a plurality of working-fluid chamberstherein by partitioning an internal space by a plurality of shoesprotruding radially inward from an inner peripheral surface of thehousing; a vane rotor having a rotor adapted to be fixedly connected toa camshaft and a plurality of radially-extending vanes formed on anouter periphery of the rotor for partitioning each of the working-fluidchambers of the housing by the shoes and the vanes to definephase-advance working chambers and phase-retard working chambers, thevane rotor being configured to phase-advance relative to the housing bysupplying hydraulic pressure to each of the phase-advance workingchambers and by discharging working oil in each of the phase-retardworking chambers and configured to phase-retard relative to the housingby supplying hydraulic pressure to each of the phase-retard workingchambers and by discharging working oil in each of the phase-advanceworking chambers, and also configured to have a cylinder structural boreformed in at least one of the plurality of vanes as a through holeextending in a direction of a rotation axis of the vane rotor; a lockmechanism having a lock member slidably installed in the cylinderstructural bore and a biasing member for biasing the lock member in itsextended direction from the vane rotor, the lock mechanism beingconfigured to permit the lock member to be displaced in its retracteddirection against a biasing force of the biasing member by hydraulicpressure acting on the lock member; an engaging recess formed in thehousing so as to oppose the lock member, for restricting rotary motionof the vane rotor relative to the housing by bringing the lock memberinto engagement with the engaging recess with sliding motion of the lockmember in the extended direction; a helical torsion spring attached atone end to the vane rotor and attached at the other end to the housing,for exerting a biasing force on the vane rotor and for biasing the vanerotor relative to the housing in a specified phase-change directionunder a preload of the torsion spring, adjacent coils of the torsionspring being brought into contact with each other at a part of thetorsion spring in a circumferential direction under a state where thetorsion spring is loaded; and a back-pressure relief passage throughwhich a back-pressure chamber, configured to install the biasing memberof the lock mechanism, is communicated with an exterior space of thehousing, the back-pressure relief passage configured to open toward thetorsion spring, wherein the back-pressure relief passage is provided ata predetermined circumferential position that goes across a givenangular position displaced from a spring-retainer position at which theother end of the torsion spring is attached to the housing byapproximately 90 degrees in a direction opposite to a spring-loadeddirection of the torsion spring.